The present disclosure relates to a polygon motor unit with a polygon motor and an optical scanning device and an image forming apparatus with such a polygon motor unit.
An exposure unit described below has been conventionally known as a unit with a polygon motor. In this technology, the exposure unit includes a housing which is provided with a bottom portion and a lid portion, a polygon mirror which is driven and rotated and deflects light irradiated to the circumferential surface thereof to scan a predetermined target, a polygon motor which rotates the polygon mirror, a drive circuit board and a heat pipe. The polygon mirror and the polygon motor are supported on the drive circuit board and the drive circuit board is fixed to the bottom portion of the housing. Further, a heat diffusion member is arranged on the lid portion of the housing and the heat pipe is connected between the drive circuit board and the heat diffusion member. Heat generated as the polygon motor rotates is transferred from the drive circuit board to the heat diffusion member located above along the heat pipe.
In the case of transferring the heat generated on the drive circuit board upward by the heat pipe as in the above technology, a space occupied by the exposure unit increases since a space above the polygon mirror is occupied. On the other hand, in the case of radiating heat utilizing a housing bottom side of the drive circuit board, the heat is thought to be transferred via a supporting portion by which the drive circuit board is supported on the housing bottom portion. In this case, it is desired to increase the surface area of the supporting portion to promote heat radiation. However, since the drive circuit board includes the polygon mirror, the supporting portion that also functions to position the polygon mirror is required to have high positioning accuracy. Thus, an increase of the surface area of the supporting portion leads to an increase of an area required to be processed with high accuracy, which brings about a cost increase of the exposure unit.
The present disclosure was developed in view of the above problem and an object thereof is to efficiently radiate heat from a board supporting a polygon mirror and a polygon motor for rotating the polygon mirror.